Residuum recovery from coal conversion process



United States Patent Ofice 3,519,554 Patented July 7, 1970 3,519,554 RESIDUUM RECOVERY FROM COAL CONVERSION PROCESS Harold H. Stotler, Westfield, N.J., and Michael Calderon,

Flushing, N.Y., assignors to Hydrocarbon Research,

Inc., New York, N.Y., a corporation of New Jersey Filed Apr. 8, 1968, Ser. No. 719,456 Int. Cl. Cg 1/06 U.S. Cl. 208-10 7 Claims ABSTRACT OF THE DISCLOSURE A process for the catalytic hydrocracking of a solid carbonaceous feed material by passing an oil slurry of the particulated feed with hydrogen upwardly through a catalytic reaction zone at high temperatures and pressures, such that the catalyst bed is in the ebullated state, and removing gaseous and liquid products from the reaction zone along with solids. The liquid products are separated into light distillates, middle oils, recycle and slurry oils and a residuum stream which is recycled to the reaction zone and solids-containing bottoms material which contains both residuum and heavy hydrocarbon oils. A wash liquid in which the residuum and oils have a high solubility, but which has a high volatility relative to the residuum and which is readily condensible with water at about atmospheric pressure is mixed with the bottoms material. This mixture is then separated into a first portion containing substantial amounts of wash liquid and oil and residuum and a second portion which contains essentially all of the solids along with small amounts of wash liquid and oil and residuum. The first portion if thermally and steam fractionated into pure wash liquid which is returned into the process and oil and residuum which is subjected to further downstream treatment. The second portion is mixed with water at about 180 F. and is then fractionated at reduced pressures such that the water contained in the mixture vaporizes and steam strips the wash liquid from the mixture. This results in a solids water slurry and a water-wash liquid mixture from which the wash liquid may easily be recovered and reused in the process.

BACKGROUND OF THE INVENTION This invention pertains to the field of conversion of a carbonaceous solid material to valuable hydrocarbon liquids and gases. More specifically, it pertains to the catalytic hydrogenation of coal and similar materials to liquid hydrocarbons of the nature of light distillates, middle oils and residuum.

Numerous processes for the conversion of solid carbonaceous materials, such as coal, bituminous and subbituminous coals, anthracite, lignite and peat are known to the art. Recently, substantial improvements in the catalytic hydrocracking of these'materials to valuable liquid and gaseous hydrocarbons have been developed, particularly as disclosed in the Johanson Pat. Re. 25,770 and the Schuman et al. U.S. Pat. No. 3,321,393. In such processes, a feed material such as coal, is pulverized and dried and is then fed in a slurry oil upwardly with hydrogen through a catalytic bed at high temperatures and pressures. The velocity of the gas and the slurry feed are such that the catalyst is put in a random state of motion and the overall catalytic bed is expanded to a volume substantially greater than its original volume. Such liquid phase expanded beds have been given the designation ebullated. Typical conditions used for such processes are temperatures in the range from about 700 to about 900 F., hydrogen pressures in the range from about 1000 to about 4000 pounds per square inch and coal throughputs from about 10 to about 50 pounds per hour per cubic foot of reactor. These contacting systems have demonstrated superior effectiveness in the conversion of coal, specifically with respect to the yield of valuable products from the coal.

In such processes, the liquid efiluent contains solids consisting of unconverted coal and ash. It is usual to remove most of the distillate oil contained in the liquid eflluent from the residuum and solids by conventional fractionation methods. However, the bottoms stream from such fractionation will contain all of the net residuum from the process, i.e., that residuum which has not been converted even after recycle, in addition to the unreacted solids. These solids, along with the residuum and some heavy distillate oil, can be fed to a fluid coking plant wherein the residuum is thermallycracked to distillates and coke. Experience has shown that only about 30% of the residuum is cracked to distillate oils with the remainder being cracked to gas and coke. Such a loss can represent as much as 6 to 10% decrease in overall coal conversion.

Methods have now been disclosed for efficiently removing the last remnants of hydrocarbons from the solids material, whereby the hydrocarbons could be returned to the process for further conversion to valuable products. Such processes utilize the introduction of a wash liquid to the liquid product solids slurry, said wash liquid having a preferential attraction for either the oils and residuum or the solids material.

In the case where the wash liquid has a preferential attraction for the hydrocarbon oils and residuum, a major portion of the hydrocarbons are dissolved in the wash liquid, and may be easily separated from the solids. However, remnants of the wash liquid are retained with the solids and must be recovered before disposal of the solids, if the plant is to be commercially feasible. In a 100,000 barrel per day refinery, for example, about 50,000 pounds per hour of wash liquid would be lost unless a suitable recovery method is used.

Methods for the thermal fractionation of the wash liquid from the solids material have now been disclosed, however, these leave something to be desired from the standpoint of efficiency, and, also, the inherent difficulties of handling and fractionating a mixture which is mostly a concentrated slurry of particulate solids.

A second method has been disclosed whereby an aromatic wash liquid is used and a solvent for aromatics, such as sulfur dioxide, is used to dissolve and extract the aromatic wash liquid from the solids. While such extraction solvents give relatively high recoveries of wash liquid, they themselves are very expensive and usually require elaborate refrigeration, equipment and procedures for their own recovery.

Thus, while numerous methods for the use of such wash liquid and subsequent recovery have now been disclosed, there are several disadvantages inherent in these methods, which, if overcome, would result in significant improvement in coal conversion processes from the standpoint of economic feasibility.

SUMMARY OF THE INVENTION We have discovered that by the use of a hydrocarbon wash liquid, in which the oil and residuum have high solubility, but which has high volatility relative to said residuum and which is readily condensible with water at pressures in the range of atmospheric pressure, not only can a substantial increase in the recovery of the residuum and oil that would normally be retained with the solids be effected, but also essentially all of the retained wash liquid may be recovered from the solids simply by the use of water as a recovery medium.

Particularly, our invention applies to processes for converting carbonaceous feed materials to liquid and gaseous products by passing a hydrocarbon oil slurry of the dried particulate feed upwardly with hydrogen at high. temperatures and pressures through a reaction zone, which contains a bed of particulate catalyst, such that the bed is in the ebullated state.

Gaseous and liquid effluents are removed from the reaction zone. The liquid eflluent stream contains solids consisting of ash, catalyst and unconverted feed material and liquid products including residuum and heavy and middle gas oils. The liquid effluent from the reaction zone is then subjected to a primary separation step in which a major portion of the residuum and oils is removed from the efiluent. The separated residuum and oil is recycled to the reaction zone. The preliminary separation, which may be filtration or centrifuge type system, does not effect a complete separation of the solids. However, while some solids are carried over in the recycle stream, most of the solids material is removed as a slurry in the retained residuum and heavy oils. The slurry consists basically of two components. The first component contains various hydrocarbon products plus residuum material, i.e., material boiling higher than 975 F. and the second component consisting of solids from the hydrogenation step, i.e., ash and unconverted coal.

The wash liquid is then mixed with the slurry whereby substantial amounts of the hydrocarbon products and residuum dissolve in the wash liquid and the viscosity of the hydrocarbons and residuum is reduced to increase ease of handling. The wash liquid solution is then separated from the solids second component by methods such as centrifugal force type separation devices, or settling and filtration operations. The wash liquid solution containing most of the first component is then subjected to thermal fractionation and steam stripping at reduced pressure, whereby, the Wash liquid, free of the first com ponent is recovered for further use in the process. The thermal fractionation is performed in such a manner has hereinafter described, as to relatively high efficiency of separation while minimizing utility requirements. The hydrocarbon and residuum products are recovered for subsequent downstream processing.

The second component along with retained wash liquid and small amounts of the first component is then mixed with substantial amounts of water in the temperature range from about 150-200 F. The water serves not only to dilute the second component for ease in handling but also to provide the stripping medium for the subsequent recovery step. This slurry is then subjected to a thermal treatment at reduced pressure. The combination of pressure and reduced pressure causes vaporization of a portion of the water contained in the slurry, said water vapor acting as an internal steam stripping mechanism to separate the Wash liquid from the slurry. The water-Wash liquid mixture is then separated into essentially waterfree wash liquid overhead which is reused in the process and water and a bottoms material consisting of a water and solids slurry containing insignificant amounts of the wash liquid.

Thus, by the use of our invention, it is possible to obtain increased recovery of valuable hydrocarbons and residuum that would normally be lost in a coking step with maximum recovery of Wash liquid using relatively inexpensive recovery media and mechanisms.

DESCRIPTION OF THE DRAWING The drawing is a schematic flow diagram of a coal conversion process.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing, a slurry of oil and a carbonaceous solid fuel material, such as bituminous or subbituminous coal, lignite or peat, which has been pulver- 4 ized and dried at 10, hydrogen rich gas at 12 and a high concentration residuum stream at 15 is introduced to reactor 16 through line 14. The coal slurry used is normally about a 1:1 mixture of solids and oil.

The reaction zone contains a particulate hydrogenation catalyst which is in an ebullated state due to the velocity of the gas and liquid feed materials upwardly through it. Gaseous products are removed through 18 and introduced to separation tank 26, wherein any liquid materials are separated from the vapor products. The vapor products are removed through line 30 and the liquid products are removed through line 34. The liquid effiuent from the reactor is removed through line 20 to separation tank 24, wherein a separated vapor product is removed in line 28 and combined with those contained in line 30. The separated liquid products are then removed in line 32. If desired, a portion of the liquid effluent in line 20 may be used as a recycle stream in line 22 back to the reactor, usually for the purposes of providing additional liquid velocity to maintain the ebullated state of the catalyst. The liquid effluent in line 32 consists essentially of solids, residuum and heavy and middle gas oils. This efiluent is separated in separator 35 (usually a liquid cyclone) into an overhead, 15, consisting of most of the residuum and oils in the effluent and a minimal amount of solids. Overhead 15 is recycled to the reactor. The bottoms, 37, from separator 35, are introduced to fractionation step 36.

Fractionation step 36 may consist either of single or multiple stage distillation units at both atmospheric and sub-atmospheric conditions. Products are removed through line 38, said products consisting of middle oils, including kerosene, gas oils, etc., and heavier materials boiling up to about 975 F. These products may be further treated downstream using the usual type of refining processes. The bottoms material in line 40 is composed of a first component consisting essentially of residuum and heavier hydrocarbon oils and a second component consisting essentially of solids, including unconverted coal and ash. This solids oil and residuum stream is pumped by pump 42 through line 44 to heat exchangers 46 and 48, wherefrom it exits at a temperature in the range from about 400 to about 500 F. and a pressure in the range from about 150 to about 180 p.s.i.g.

The stream in line 44 is then introduced to tank 54, and mixed with hydrocarbon wash liquid at a temperature from about to about 200 F. from line 56. The wash liquid may be any suitable hydrocarbon material which has a high solvent power with respect to the oil and residuum, but which also has a high volatility relative to the residuum and is readily condensible with Water in the range about atmospheric pressure. Such hydrocarbon materials would be those boiling in the range from about F. to about 300 F. at atmospheric pressure. Typical examples of such compounds are linear and branched aliphatic compounds containing between 6 and 9 carbon atoms, cyclic aliphatic compounds containing between 6 and 8 carbon atoms and aromatic compounds, such asbenzene, toluene, ortho, meta and para xylene and ethyl benzene or combinations thereof. While the choice of the wash liquid depends on the particular economic considerations of the process, the case herein described uses benzene as the wash liquid.

Benzene is added to tank 54 at a rate between one to two volumes of benzene per volume of first component After allowing sufiicient residence time for the benzene to penetrate the pores of the solid, the mixture is removed through line 58 to separation device 60. This device may be any one of a number of liquid solid separation methods known to the art, preferably a hydro-cyclone or liquid centrifuge. A first portion composed of at least about 90% of the benzene and oil and residuum is removed through overhead line 62. After pressure reduction in valve 64, the material is introduced through line 66 to fractionator 68. The temperature in this fractionator is in the range from about 290 F. to about 330 F. and approximately to of the original benzene added is removed as vapor overhead through line 76. The remainder of the material in fractionator 68 is removed through line 70, pressure reduced through valve 72 and introduced to fractionator 74 at a temperature in the range from about 220 to about 260 F. and a pressure in the range from about atmospheric to about 30 p.s.i.g. The heat for the fractionation in fractionator 74 is supplied by heat exchange with the condensing benzene vapor at about 300 F. from fractionator 68 in line 76. This benzene liquid is then removed in line 78 at a somewhat decreased pressure and introduced to line 56 for re-use as wash liquid. An overhead benzene stream from fractionator 74 is removed as vapor in line 80. It represents about to about of the original benzene added. It is then condensed in cooler 82 and mixed with make-up benzene from line 88 in tank 86. The combined benzene streams are then introduced through line 90 to pump 114 which exits the stream into line 56 for re-introduction to the process as wash liquid.

The bottoms from fractionator 74 now consist essentially of the first component residuum and oil material with some benzene. This is removed through line 92, is pumped by pump 94 and passed in heat exchange with 300 p.s.i.g. steam in exchanger '96. The heated oil, residuum and benzene is then introduced through line 98 to steam stripper 100. Steam at 300 p.s.i.g. is introduced to stripper 100 through line 102. An overhead water vaporcovered, i.e., at least 85%, plus traces of benzene. The A recovery of this first component represents one of the major advantages of our invention.

The bottoms material from separator 60 consist of about 80% solids material, which is all of the solid material which had been contained in line 58. The remaining 20% is a mixture of oil and residuum material and benzene. This slurry is introduced through line 118 to tank 120, wherein it is mixed with approximately an equal amount by weight of water which is obtained through pump 50 and line 52, after heat exchange with the solids and residuum material in exchanger 48 and water recycled in line 150. This water is at a temperature of about 180 F.

After sufiicient mixing time, the slurry is removed through line 122 and pressure reduced in reducing valve 124. It is then introduced to thermal fractionator 126. Heat is supplied to the fractionator by introducing 50 Ap.s.i.g. steam in line 136 and removing it through line 138. A benzene water vapor mixture is removed at overhead through line 132 and the solids, remaining residuum, oil, benzene and water are removed as bottomsthrough line 128 and introduced to a second thermal fractionation unit 130. Heat is supplied to unit 130 by introducing 50 pounds steam through line and withdrawing it through 142. Unit 130 as a result of its series relationship with unit 126 is operated at a somewhat lower pressure. Therefore, the overhead water vapor and the benzene stream in line 134 has a somewhat higher proportion of water than the mixture contained in line 132. The stream in line 134 is combined with that in line 132. The bottoms material from unit 130 contains essentially all of the second component solids and water along with traces of benzene and is removed through line as the char product from the plant. If desired, it may be subjected to an additional thermal fractionation similar to those carried out in units 126 and 130. It is understood that the number of thermal fractionating units is dependent solely on the design parameters of the system, and it is a relatively simple chemical engineering calculation to determine the number of such units required to optimize the process. Normally, if two or three such units are used in series, the temperature of each unit would be in the range from about 200 to about 250 F. with each unit operating at successively lower pressures within the range from about atmospheric to about 40 p.s.i.g.

The combined benzene-water vapor overhead fractions from the thermal fractionation units contain between about 5 to about 15 of the original benzene added. The overhead is cooled in cooler 144 and then introduced through line 146 to separation drum 1 48. Water-free benzene is removed from drum 148 through line 152 and introduced to the benzene obtained from the make-up drum 86 and separation tank 110, for re-use in the sys tern. Water is removed from separation drum 148 through line 150, is combined with that water removed from separation drum 110 in line 116, and is then recycled through line back to line 52 for re-use in the system.

EXAMPLE I.BENZENE WASH LIQUID RECOVERY Material recovery Percent Percent Percent of initial of initial of initial oil and Conditions Line benzene solids residuum p.s.i.g., 350 F 58 100 100 100 110 p.s.i.g., 350 F... 62 90 90 Fractionator 68, 60 p.s. .g.,

310 F 76 5 p.s.i.g., 245 F 80 02 5 p.s.i.g., 330 F 106 104 Drum 110, 2 p.s.l.g., F 112 116 Tank 120, 110 p.s.i.g.,

230 F 118 3 thermal units, 33 p.s.i.g'., 146

12 p.s.i.g., 8 p.s.i.g., all at 230 F 145 Drum 148, 2 p.s.i.g., 165 F 152 150 Total lost 0. 12 10 1 Lost Example I shows a detailed summary of the step by step recovery of benzene, solids, oil and residuum and water for the process as described above. It also outlines the particular temperature and pressure conditions used at various stages throughout the process. The data shown applies to processes using a benzene to heavy oil ratio of both 1:1 and 2:1. The process differences between the use of these two ratios are very slight, requiring only minor changes in heat exchange requirements. Based on the above data, for a 100,000 b.p.s.d. refinery using Illinois coal, the material obtainedas bottoms in line 40 would consist of about 500,000 pounds per hour each of solids and of oil and residuum component. Using a 1:1 ratio of benzene to oil, 500,000 pounds per hour of benzene would be added in tank 54 as wash liquid. Thus, it is seen that in such a commercial process, only about 600 pounds per hour of benzene would be lost and the recovery of residuum and oil would be at least 400,000 pounds per hour. It is known that if such residuum were processed directly in a fluid coking plant, as opposed to applicants invention, only about a 30% recovery could be expected.

Although the above example and discussion discloses a preferred mode of embodiment of applicants invention, it is recognized that from such disclosure, many modifications will be obvious to those skilled in the art and it is understood, therefore, that applicants invention is not limited to only those specific methods, steps or combinations or sequence of method steps described, but covers all equivalent steps or methods that may fall within the scope of the appended claims.

We claim:

1. In combination with a process for conversion of solid carbonaceous feed materials to valuable liquid and gaseous products of the type wherein a slurry of the dry particulate feed in a hydrocarbon oil is passed upwardly with hydrogen at high temperature and pressure through a reaction zone containing a bed of particulate catalyst, the velocities of the feed slurry and gas being such as expand the bed and cause it to be in an ebullated state and wherein liquid and gaseous eflluent streams are withdrawn from the reaction zone, the liquid effluent stream containing solids consisting of ash, catalyst and unconverted feed material and liquid products including residuum and heavy and middle gas oils and wherein said liquid effluent stream is subjected to a primary separation step wherein a substantial amount of the solids are separated to form a high concentration residuum stream having a minimum solids concentration which is recycled to the reaction zone and a concentrated slurry stream having a high concentration of solids, and wherein the concentrated slurry is at superatmospheric pressure and contains a residuum and hydrocarbon product first component and a solids second component and wherein the slurry is subjected to a separation step wherein some of the first component is removed from the second component, the improvement which comprises increasing the amount of the first component removed from the second component by:

(a) introducing a hydrocarbon wash liquid to the concentrated slurry, the wash liquid being a solvent in which the first component has a high solubility and which has a high volatility relative to the first component, but which is readily condensible with water at a pressure about atmospheric;

(b) mixing the liquid product and wash liquid; and

then

(c) separating the mixture from step (b) into a first portion containing major amounts of the first component and the wash liquid and essentially no second component and a second portion containing essentially all of the second component and minor amounts of the first component and wash liquid; and then ((1) fractionating and steam stripping the first portion at reduced pressure into essentially wash liquid-free first component which is suitable for further downstream processing and high purity wash liquid which is recovered and returned to the process;

(e) mixing warm water with the second portion from step (c); and then (f) heating the mixture from step (e) at reduced pressure such that some of the water and essentially all of the Wash liquid contained therein vaporize, and removing from the heating step the wash liquid-water vapor and an essentially wash liquid-free slurry of water and solid product; and

(g) separating the wash liquid-water vapor mixture into wash liquid which is returned to the process and water.

2. The process as claimed in claim 1 wherein the feed material is a fuel selected from the group consisting of bituminous and sub-bituminous coal, anthracite, lignite and peat.

3. The process as claimed in claim 1 wherein the wash liquid is selected from the group consisting of linear and branched aliphatic compounds containing between 6 to 9 carbon atoms, cyclic aliphatic compounds containing between 6- and 8 carbon atoms and aromatic compounds including benzene, toluene, ortho, meta and para xylene and ethyl benzene and combinations thereof.

4. The process as claimed in claim 3 wherein the first portion is fractionated by reducing the pressure on the first portion and then introducing it to a first fractionation unit, removing a hot, high purity wash liquid overhead from the first unit and a bottoms consisting of the first component with a decreased amount of wash liquid, pressure reducing said bottoms and introducing it to a second fractionation unit which is at a lower temperature than the first unit and passing the hot overhead from the first unit in heat exchange with the bottoms in the second unit whereby additional amounts of wash liquid are vaporized from said bottoms and whereby essentially all of the heat required for the vaporization in the second unit is supplied by the heat exchange.

5. The process as claimed in claim 4 wherein the ratio of the first component to the second component On a weight basis is about 1:1.

6. The process as claimed in claim 5 wherein the liquid product is a bottoms material from a vacuum distillation unit and which comprises:

(a) compressing the liquid product to a pressure in the range from about to about p.s.i.g. and adjusting the temperature of the liquid product to within the range from about 400 to about 500 F. and then;

(b) mixing the liquid product with a sufficient amount of benzene at a temperature from about 180 F. to 200 F. to dissolve essentially all of the first component contained in the liquid product in the benzene; and then (c) separating the mixture by centrifugation into a first portion which contains at least about 80% each of the first component and of the benzene and a second portion which contains essentially all of the second component and not more than about 20% each of the first component and the benzene;

(d) reducing the pressure of the first portion to a range from about 50 to about 70 p.s.i.g. and then fractionating the first portion in a first fractionation step at a temperature in the range from about 300 to about 330 F. to product a bottoms material and an overhead, said overhead consisting of pure benzene representing from about 20 to about 30% of the original benzene added; and then (e) introducing the bottoms material to a second fractionation step at a pressure within the rangefrom about atmospheric to about 25 p.s.i.g. and a temperature within the range from about 230 to about 260 F. and wherein said bottoms material is heated by contacting it in heat exchange relationship with the benzene overhead from the first fractionation step, whereby essentially all of the heat required for the second fractionation step is supplied by the heat exchange; and then (f) returning the benzene overhead from the first fractionation stage after the heat exchange step to the process for further use, and removing from the second fractionation step an overhead benzene vapor which constitutes between about 50 to about 60% of the original benzene added and returning the vapor to the process for further use and a bottoms fraction; and then (g) heating the bottoms fraction to a temperature in the range from about 300 to about 360 F. and introducing the heated fraction to a stream stripper where it is contacted wtih steam to produce a bottoms which consists essentially of at least 80% of the first component and traces of benzene and an overhead which consists of water vapor and benzene, the 'benzene in the overhead constituting between about 10 to about 20% of the original benzene added and then separating the benzene from the water vapor and returning the benzene to the process;

(h) mixing the second portion from step (c) with water at about 180 F., the amount of water being approximately equal in weight to the amount of the second component contained in the second portion, to produce a slurry; and then (i) fractionating the slurry in three stages in series, the temperature of each stage being in the range from 9 10 about 220 to about 250 F. each stage operating at amount of benzene originally added is between about 1 successively lower pressures within the range from to about 2 volumes for each volume of liquid product. about atmospheric to about 40 p.s.i.g., whereby an overhead stream consisting of Water vapor and ben- References C'ted zene vapor product, the benzene constituting about 5 UNITED STATES PATENTS 5 to 15% of the original benzene added and a bot- Re 25,770 4/1965 Johauson toms material which contains essentially all of the 3 321 5/1967 Schuman et 1 1 second component along with water and traces of 3 030 297 4 19 2 Sh d 203 10 benzene are Obtained; and then S.N. 700,485 4/1969 Hemminger et al. 20810 (j) separating the benzene vapor product from the 10 v Water and returning said benzene to the process. O KE'EFE Asslstant Exammer 7. The process as claimed in claim 6 wherein the DELBERT E. GANTZ, Primary Examiner 

